The present invention relates to a manifold, and more particularly a supply or receiving tank in a heat exchanger, including a hollow body provided with a plurality of wall apertures for the insertion of heat exchanger tubes.
Heat exchangers of the above mentioned type, employed for example as condensers or radiators in a vehicle, are in principle manufactured by two methods, i.e. soldering or mechanical expansion of the tubes after their insertion into the manifold. Both methods are at the present time characterized by several problems related to the manufacture of a reliable, leakage-proof connection having satisfactory mechanical strength. Especially the so-called solderfree radiators normally have to be provided with packing rings or possibly glue in the connections as a supplement to expansion of the tubes in order to assure an acceptable, leakage-proof contact.
DE 2448332 describes a heat exchanger for vehicles based upon a mere expansion connection between tubes and manifold without use of supplementary rubber packings. The construction is characterized by a precisely specified interaction between a number of parameters such as wall thickness, tube diameter, material strength, length of support and others expressed in empirical formulas. This construction requires high tolerances from the components, and furthermore it has obvious limitations with regard to free choice of materials, wall thickness, tube diameter, etc.
A further disadvantage of such known construction is represented by the process employed for making fastening apertures in the tube wall. The wall is "knocked down" and pressed and drawn further inwards to form a collar or flange which ensures the necessary support or backing area for fastening of the heat exchanger tubes. The height of the collar is related to the wall thickness of the manifold, which gives poor possibilities of achieving an adequate collar height on thin-walled manifolds due to the limited material mass which can be transferred in the deformation zone.
Limited material flow is also the disadvantage of the so-called T-drill or Flow-drill processes, where by means of special tools the manifold tube is perforated under formation of a low collar. Depending on the type of tool applied, this low collar is formed on the underside or both on the underside and partly also on the outside of the manifold. In those cases where the collar protrudes inwards into the manifold, the available, free cross-section of the manifold is reduced and an increased pressure drop in the heat exchanger arises due to turbulent currents in the manifold.
Additionally to the above mentioned disadvantages, also several other problems arise by soldering of the heat exchanger tubes to such manifolds. Because of the short collar a penetration of soldering material and flux along the tubes into the manifold occurs quite frequently, which further contributes to the reduction of the available, free cross-section. Flux entrapped in this way is difficult to remove and has a corrosion promoting effect on the components. Furthermore, it is difficult to achieve a tight and stable soldering connection because of the short soldering length available. In the case of inwardly protruding soldering collars it is difficult to control the amount of heat, since heating takes place mainly by means of heat conduction through the tubes, since the soldering zone is concealed in the manifold. Overheating of the tubes and mechanical weakening of the connection as a result therefore represent an imminent danger of a large reject rate by manufacture of heat exchangers according to this principle.